With a display panel such as a liquid crystal panel or an organic EL panel, an image or video is displayed using a collection of pixels having R (red), G (green), and B (blue) sub-pixels, which correspond to the three primary colors of light. With this kind of display panel, in general, display unevenness sometimes occurs due to variations in machining accuracy in the manufacturing step. The display unevenness is largely divided into luminance unevenness and color unevenness.
Luminance unevenness occurs in the case where there is a difference in absolute brightness between nearby pixels. On the other hand, color unevenness occurs in the case where the relationship between the relative brightnesses of R, and B in an individual pixel differs between nearby pixels.
In particular, due to the fact that it is difficult to make the thickness of an organic compound layer for each pixel even, organic EL panels have a characteristic such that display unevenness caused by the layer thickness of the organic compound layer being uneven is likely to occur.
As a countermeasure against this, Patent Document 1 has proposed a luminance measurement method that aims to improve image quality of a display panel by illuminating pixels of the display panel, performing image capture using a camera including a solid-state image sensor, and measuring the luminance of the pixels so as to detect display unevenness and correct the detected display unevenness.
However, in the case of capturing an image of a display panel in which pixels are aligned periodically with a solid-state image sensor camera in which imaging pixels on an image capture plane are aligned periodically, moiré, which is also referred to as “interference fringe,” appears in the captured image due to misalignment occurring between the period in which the pixels are aligned and the period in which the imaging pixels are aligned.
When the luminance of the pixels is measured based on the captured image in which moiré appears, the influence of the moiré needs to be suppressed due to the fact that the luminance cannot be accurately measured due to pixels at positions corresponding to the moiré on the display panel being measured as being dark.
As a countermeasure against this, Patent Document 2 discloses a method of converting signals of a spatial axis of an image in which moiré appears into signals of a frequency axis, removing frequency components that correspond to the moiré from the signals of the frequency axis, and thereafter re-converting the signals of the frequency axis from which the frequency components corresponding to the moiré have been removed into the signals of the spatial axis.
According to this moiré removal method, signals of the spatial axis of an image in which moiré with a constant period appears are converted into signals of a frequency axis, whereby the frequency components corresponding to the moiré can be removed.